U.S. patent number 6,032,639 [Application Number 09/140,326] was granted by the patent office on 2000-03-07 for diagnosis for fuel system of internal combustion engine.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Kenichi Goto, Hideyuki Tamura.
United States Patent |
6,032,639 |
Goto , et al. |
March 7, 2000 |
Diagnosis for fuel system of internal combustion engine
Abstract
A diagnostic system for a fuel system of an internal combustion
engine such as direct-injection gasoline engine monitors a pressure
deviation of a actual fuel pressure sensed by a fuel pressure
sensor from a desired fuel pressure in a feedback fuel pressure
control, and thereby detects abnormality in the fuel system. When
the pressure deviation continues to be outside a normal range, a
diagnostic controller commands engine operation in a homogeneous
stoichiometric combustion mode, and monitors a feedback correction
quantity in a feedback stoichiometric air fuel control during the
engine operation in the homogeneous stoichiometric combustion mode.
The controller attributes the abnormality to the fuel pressure
sensor if the feedback correction quantity of the air fuel ratio is
fixed to an upper limit or a lower limit.
Inventors: |
Goto; Kenichi (Kanagawa,
JP), Tamura; Hideyuki (Yokohama, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
16932493 |
Appl.
No.: |
09/140,326 |
Filed: |
August 26, 1998 |
Foreign Application Priority Data
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|
|
|
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Aug 28, 1997 [JP] |
|
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9-232007 |
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Current U.S.
Class: |
123/295; 123/359;
123/690; 123/479 |
Current CPC
Class: |
F02D
41/222 (20130101); F02D 41/3863 (20130101); F02D
41/3818 (20130101); F02D 41/3076 (20130101); F02D
2041/224 (20130101); F02D 41/3029 (20130101); F02D
2200/0602 (20130101); F02D 41/187 (20130101); F02D
2041/389 (20130101); F02D 2041/223 (20130101); F02D
2250/31 (20130101) |
Current International
Class: |
F02D
41/22 (20060101); F02D 41/38 (20060101); F02D
41/30 (20060101); F02D 041/22 (); F02B
017/00 () |
Field of
Search: |
;123/295,479,690,198D,359 ;73/119A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
5-069374 |
|
Sep 1993 |
|
JP |
|
5-321783 |
|
Dec 1993 |
|
JP |
|
Other References
"Toyota Corona Premio", New Model Manual, (1996), pp. 1-59 (No
translation) ..
|
Primary Examiner: Argenbright; Tony M.
Assistant Examiner: Castro; Arnold
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A diagnostic control method for detecting malfunction in a fuel
system for a fuel injection type internal combustion engine, the
method comprising;
a pressure sensing step of sensing an actual fuel pressure with a
fuel pressure sensor;
a pressure controlling step of performing a feedback fuel pressure
control to reduce a pressure deviation of the actual fuel pressure
sensed by the fuel pressure sensor from a desired fuel
pressure;
an abnormality detecting step of detecting abnormality in the fuel
system by monitoring the actual fuel pressure;
a richer combustion mode effecting step of effecting a feedback air
fuel ratio control in a predetermined richer combustion mode if the
abnormality is detected; and
a diagnosing step of judging whether to attribute the abnormality
to the fuel pressure sensor, by monitoring performance of the
feedback air fuel control in the richer combustion mode.
2. The diagnostic method according to claim 1 wherein the
predetermined richer combustion mode is a homogeneous
stoichiometric charge combustion mode, the pressure sensing step is
carried out by sensing the actual fuel pressure in a fuel delivery
passage for supplying fuel from a fuel pump to a fuel injector, the
abnormality detecting step is carried out by checking whether the
sensed fuel pressure is settled down to the desired fuel pressure
and judging that the abnormality exists when the sensed fuel
pressure is not settled down to the desired fuel pressure, and the
diagnosing step is carried out by discriminating a malfunction in
the fuel pressure sensor from a malfunction nonattributable to the
fuel pressure sensor in accordance with a ratio deviation of an
actual air fuel ratio from a theoretical air fuel ratio.
3. The diagnostic method according to claim 1 wherein the
abnormality detecting step is carried out by monitoring the
pressure deviation of the actual fuel pressure from the desired
fuel pressure, and the diagnosing step is carried out by monitoring
a signal produced in the feedback air fuel ratio control.
4. The diagnostic method according to claim 3 wherein the richer
combustion mode is a homogeneous stoichiometric charge combustion
mode and wherein the diagnosing step is carried out by monitoring a
control parameter which is one of a ratio deviation of an actual
air fuel ratio from a desired air fuel ratio of the richer
combustion mode and a feedback correction quantity of the feedback
air fuel control.
5. The diagnostic method according to claim 4 wherein the richer
combustion mode effecting step is carried out by forcibly changing
over engine operation from a lean combustion mode to the
homogeneous stoichiometric combustion mode if the abnormality is
detected.
6. The diagnostic method according to claim 5 wherein the lean
combustion mode comprises a stratified charge combustion mode.
7. The diagnostic method according to claim 4 wherein, in the
abnormality detecting step, an abnormality signal indicating
abnormality in the fuel system is produced when the pressure
deviation of the sensed fuel pressure from the desired fuel
pressure remains outside a predetermined normal range for a time
duration equal to or longer than a predetermined time length.
8. The diagnostic method according to claim 7 wherein the
abnormality detecting step comprises a step of comparing the
pressure deviation with a predetermined deviation value to
determine whether the pressure deviation is outside the normal
range, and the predetermined deviation value is varied in
accordance with the desired fuel pressure.
9. The diagnostic method according to claim 4 wherein the
diagnosing step comprises a step of producing a first warning
signal indicative of malfunction in the fuel pressure sensor when
the feedback correction quantity of the air fuel ratio control is
fixed to one of predetermined upper and lower limit values, and
otherwise producing a second warning signal indicating that the
abnormality is not attributable to the fuel pressure sensor.
10. The diagnostic method according to claim 4 wherein the
diagnosing step comprises a step of determining whether the
pressure deviation is positive, and whether a correction quantity
deviation of the feedback correction quantity from a predetermined
reference value is positive, and producing a first warning signal
when one of the pressure deviation and the correction quantity
deviation is negative and the other of the pressure deviation and
the correction quantity deviation is positive, and a second warning
signal when the pressure deviation and the correction quantity
deviation are both positive, and when the pressure deviation and
the correction quantity deviation are both negative.
11. A diagnostic control system for detecting malfunction in a fuel
system for a fuel injection type internal combustion engine,
comprising:
a fuel pressure sensor for sensing an actual fuel pressure for the
engine;
a pressure controlling section for performing a feedback fuel
pressure control to reduce a pressure deviation of the actual fuel
pressure sensed by the fuel pressure sensor from a desired fuel
pressure;
an abnormality detecting section for detecting abnormality in the
fuel system by monitoring the actual fuel pressure;
a richer combustion mode effecting section for effecting a feedback
air fuel ratio control in a predetermined richer combustion mode if
the abnormality is detected; and
a diagnosing section of judging whether the abnormality is
attributable to the fuel pressure sensor, by monitoring performance
of the feedback air fuel control in the richer combustion mode.
12. The diagnostic control system according to claim 11 wherein the
richer combustion mode is a homogeneous stoichiometric charge
combustion mode, the abnormality detecting section monitors the
pressure deviation of the actual fuel pressure from the desired
fuel pressure and produces an abnormality signal indicating
abnormality in the fuel system when the pressure deviation of the
sensed fuel pressure from the desired fuel pressure remains outside
a predetermined normal range for a time duration equal to or longer
than a predetermined time length, and the diagnosing section
monitors a control parameter which is one of a ratio deviation of
an actual air fuel ratio from a theoretical air fuel ratio and a
feedback correction quantity of the feedback air fuel control.
13. The diagnostic control system according to claim 12 wherein the
diagnosing section produces a first warning signal indicative of
malfunction in the fuel pressure sensor when the feedback
correction quantity of the air fuel ratio control remains outside a
predetermined normal range one-sidedly for a duration equal to or
longer than a predetermined time length, and otherwise producing a
second warning signal indicating that the abnormality is not
attributable to the fuel pressure sensor.
14. The diagnostic control system according to claim 12 wherein the
richer mode effecting section forcibly changes over engine
operation from a lean combustion mode to the homogeneous
stoichiometric combustion mode when the abnormality is detected,
and wherein the system further comprises an output device for
receiving the first and second warning signals, and wherein the
output device is a warning indicator.
15. The diagnostic system according to claim 12 wherein the fuel
pressure sensor is arranged to sense the fuel pressure in a fuel
delivery passage for supplying fuel under pressure from a high
pressure fuel pump to a fuel injector for injecting fuel directly
into a combustion chamber of the engine.
16. An engine system comprising:
an internal combustion engine;
a fuel system comprising a fuel injector for supplying fuel to the
engine, and a fuel pump for supplying the fuel under pressure to
the fuel injector through a fuel delivery circuit;
a first input device for producing a first input signal
representing a sensed actual fuel pressure in the fuel delivery
circuit; and
a controller for performing a feedback fuel pressure control to
reduce a pressure deviation of the sensed actual fuel pressure from
a desired target fuel pressure (tFP), for detecting abnormality in
the fuel system by monitoring the pressure deviation, for
commanding a changeover of combustion in the engine from a lean
combustion mode to a richer combustion mode to effect a feedback
air fuel ratio control if the abnormality is detected, and for
judging whether the abnormality is attributable to the fuel
pressure sensor, by monitoring a feedback correction quantity of
the feedback air fuel control in the richer or combustion mode.
17. The engine system according to claim 16 wherein the richer
combustion mode is a homogeneous stoichiometric combustion mode,
the system further comprises a second input device for producing a
second input signal representing an engine operating condition of
the engine, and a third input device for determining an actual air
fuel ratio of the engine, and the controller is configured to
change over an engine operating mode between the first combustion
mode and the homogeneous stoichiometric charge combustion mode in
accordance with the engine operating condition by controlling the
fuel injection system, and to perform a feedback stoichiometric air
fuel ratio control to reduce a ratio deviation of the actual air
fuel ratio from a theoretical air fuel ratio toward zero when the
engine is operated in the homogeneous stoichiometric mode, and
wherein the first combustion mode is a stratified charge combustion
mode.
18. The engine system according to claim 17 wherein the fuel system
comprises the fuel injector for injecting the fuel directly into a
combustion chamber of the engine, the fuel pump which is a high
pressure pumpdriven by the engine, a high pressure regulator for
regulating the fuel pressure supplied to the fuel injector in
response to a pressure control signal produced by the controller, a
fuel tank, a low pressure fuel pump driven by an electric motor,
for supplying the fuel from the tank to the high pressure pump.
19. The engine system according to claim 17 wherein the controller
produces a first warning signal indicative of malfunction in the
fuel pressure sensor when the feedback correction quantity of the
feedback stoichiometric air fuel ratio control remains outside a
predetermined normal range on one side of the predetermined normal
range for a time duration equal to or longer than a predetermined
time length, and otherwise the controller produces a second warning
signal indicating that the abnormality is not attributable to the
fuel pressure sensor, and wherein the system further comprises an
output device for receiving the first and second warning
signals.
20. The engine system according to claim 19 wherein the output
device comprises a warning indicator for providing perceptible
diagnostic message in response to one of the first and second
warning signals.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine, and
more specifically to a diagnostic system or method for a feedback
fuel pressure control system for an engine, such as a direct
injection type engine or a lean burn engine.
Recently, the technique of in-cylinder direct fuel injection in a
spark ignition engine such as a gasoline engine is under
development to improve the fuel efficiency by selectively using
stratified charge combustion in a partial load region. In a
conventional engine of a type injecting gasoline into the intake
port, the air fuel mixture is transported to the combustion
chamber. By contrast, a direct injection type engine can avoid
adverse influence of transportation (distance/velocity) lag of
fuel, on transient driving performance, and emission
performance.
A direct injection engine of one conventional example is equipped
with a high pressure fuel pump for increasing the fuel pressure for
efficient fuel atomization, and a fuel pressure sensor used for
feedback-controlling the fuel pressure to a desired fuel pressure
determined in accordance with engine operating conditions. (as
disclosed in Japanese Utility Model Provisional (Kokai) Publication
No. 5(1993)-69374; "TOYOTA CORONA PREMIO", New Model Manual,
September 1996, pages 1.about.59; or Japanese Patent Provisional
(Kokai) Publication No. 5(1993)-321783).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide diagnostic
method and system capable of making accurate diagnosis on a fuel
system for an internal combustion engine.
Specifically, the diagnostic method and system according to the
present invention is arranged to discriminate various malfunctions
beyond conventional detection of decisive failure such as wire
disconnection or short-circuit in circuitry of a fuel pressure
sensor and a driving solenoid for a fuel pump in a conventional
diagnostic system.
According to the present invention, a diagnostic control method or
system (or apparatus) for detecting malfunction in a fuel system
for an internal combustion engine, comprises;
a constituent element for sensing an actual fuel pressure;
a pressure controlling element of performing a feedback fuel
pressure control to reduce a pressure deviation of the sensed
actual fuel pressure from a desired fuel pressure;
an abnormality detecting element of detecting abnormality in the
fuel system by monitoring the actual fuel pressure;
a richer combustion mode effecting element of effecting a feedback
air fuel ratio control in a richer combustion mode such as a
homogeneous stoichiometric charge combustion mode if the
abnormality is detected; and
a diagnosing element of judging whether or not the abnormality is
attributable to the process of fuel pressure sensing, by monitoring
performance of the feedback air fuel control during the engine
operation in the richer combustion mode.
This diagnostic control method or system can accurately detect
malfunction in the fuel system by monitoring behavior in both the
fuel pressure control system and the air fuel ratio control system,
so that the system can readily protect the driveability against
abnormal conditions and reduce the time required for repair.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing an engine system according to
one embodiment of the present invention.
FIG. 2 is a flowchart of a feedback fuel pressure control routine
performed by a control unit in the engine system of FIG. 1.
FIG. 3 is a flowchart of a diagnosis routine performed by the
control unit of FIG. 1.
FIG. 4 is a graph showing a characteristic of a fuel pressure
sensor in the engine system of FIG. 1.
FIG. 5 is a graph showing a basic characteristic of a high pressure
regulator in the engine system of FIG. 1.
FIG. 6 is a schematic view showing one practical example of an
engine system according to the embodiment of the present
invention.
FIG. 7 is a block diagram showing a diagnostic control system
formed by the control unit shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an engine system according to one embodiment of the
present invention. The engine system comprises an internal
combustion engine 1 as a main component, and other components. In
this example, the engine 1 is used as a prime mover for a
vehicle.
As shown in FIG. 1, the engine 1 is provided, for each cylinder,
with a solenoid-operated fuel injector 2 for injecting fuel
directly into a combustion chamber 3, at least one intake port 4
having an intake valve 5, a spark plug 6, and at least one exhaust
port 8 having an exhaust valve 7.
In this example, the engine 1 is a direct injection type spark
ignition internal combustion engine. The fuel injector 2 produces
an air fuel mixture by injecting fuel into fresh intake air
introduced into the combustion chamber 3 through the intake port 4
and the intake valve 5, and the spark plug 6 ignites the air fuel
mixture by means of an electric spark. Exhaust gas is carried away
from the combustion chamber 3 through the exhaust port 8 and the
exhaust valve 7, and discharged to the outside through a catalytic
converter and a muffler.
In this example, a combustion mode of the engine 1 is changed over
between a stratified charge combustion mode and a homogeneous
charge combustion mode. In the stratified combustion mode, the
injector 2 injects fuel during the compression stroke so as to
produce a stratified combustible mixture closely around the spark
plug 6. In the homogeneous combustion mode, fuel is injected during
the intake stroke so as to produce a homogeneous air fuel mixture.
This engine system changes over the combustion mode between the
stratified combustion mode and the homogeneous combustion mode in
accordance with one or more engine operating conditions.
A low pressure fuel pump (or first fuel pump) 10 draws fuel from a
fuel tank 9 and supplies fuel under relatively low pressure to a
high pressure fuel pump (or second fuel pump) 14 through a fuel
filter 12 disposed in a lower pressure fuel passage at a position
dividing the lower pressure fuel passage into an upstream section
11A extending from the first pump 10 to the filter 12, and an
upstream section 11B extending from the filter 12 to the high
pressure fuel pump 14. A low pressure regulator 13 is disposed in a
fuel passage branching off from the downstream passage section 11B
and extending to the fuel tank 9. By the low pressure regulator 13,
the pressure of the fuel supplied to the high pressure fuel pump 14
is held at a predetermined constant low pressure.
The high pressure fuel pump 14 of this example is driven by a crank
shaft or a cam shaft of the engine 1 directly or through gearing or
a belt. The high pressure fuel pump 14 receives the lower pressure
fuel through the fuel passage section 11B from the low pressure
pump 10, and increases the fuel pressure to a high pressure level.
A high pressure regulator 16 controls the pressure of the fuel
discharged into a high pressure fuel passage 15 from the high
pressure pump 14, and thereby serves as a controlling element of a
fuel pressure control system for controlling the fuel pressure
supplied to the fuel injector 2. In this example, the high pressure
regulator 16 is combined with the high pressure pump 14 into a
single unit. The high pressure fuel passage 15 supplies the fuel
under the controlled pressure to each fuel injector 2. The high
pressure regulator 16 of this example has a duty solenoid. This
fuel system can control the fuel pressure supplied to the injectors
2 to a desired fuel pressure by controlling a duty ratio of the
duty solenoid in a manner of a duty factor control system.
A control unit 17 controls each injector 2 by sending a pulse
signal having a controlled pulse width determined in accordance
with one or more engine operating conditions. In response to the
pulse signal, each injector 2 injects the fuel of the pressure
controlled at the desired fuel pressure, into the corresponding
combustion chamber 3 at the fuel injection timing. The control unit
17 of this example includes, as a main component, a
microcomputer.
Input information needed by the control unit 17 is collected by an
input section. The input section comprises input devices for
collecting input information by sensing various operating
conditions of the engine and the vehicle or by receiving driver's
command. From the input section, the control unit 17 receives
information for various control operations. In the example shown in
FIG. 1, the input section comprises a crank angle sensor 18 for
sensing the crank angle of the engine 1, an air flow meter (or air
flow sensor) 19 for sensing an intake air quantity, a fuel pressure
sensor 20, and an air fuel ratio sensor (or oxygen sensor) 21
disposed on the downstream side of the exhaust manifold, for
sensing the oxygen content in the exhaust gas to determine an
actual air fuel ratio. The crank angle sensor 18 is used for
sensing the engine speed for the fuel injection control. The crank
angle sensor 18 is further used for sensing the revolution speed of
the high pressure fuel pump 14. The fuel pressure sensor 20 senses
the fuel pressure in the high pressure fuel passage 15 extending
from the high pressure pump 14 to the injectors 2. Signals produces
by these sensors are delivered to the control unit 17.
In accordance with the input information, the control unit 17
controls the fuel injection quantity by controlling the pulse width
of the fuel injection pulse signal to each injector 2, and further
controls the fuel injection timing.
The control unit 17 further control the fuel pressure as shown in
FIG. 3.
FIG. 2 shows a feedback fuel pressure control routine.
At a step S1, the control unit 17 calculates a desired target fuel
pressure tFP in accordance with the engine speed Ne and an engine
operating parameter, such as a fuel injection quantity TI,
indicative of an engine load.
At a step S2, the control unit 17 reads an actual fuel pressure FP
sensed by the fuel pressure sensor 20.
At a step S3, the control unit 17 determines a pressure deviation
.DELTA.P of the actual fuel pressure FP from the desired fuel
pressure tFP, and further calculates, from the pressure deviation,
a feedback pressure control quantity according to a predetermined
control law (or control action) such as a PID control law.
At a step S4, the control unit 17 produces a fuel pressure control
signal representing the feedback fuel pressure control quantity,
and sends the fuel pressure control signal to the duty solenoid in
the high pressure regulator 16 of the high pressure fuel pump 14.
The discharge fuel quantity is thus controlled in accordance with
the feedback pressure control quantity. In this example, a feedback
fuel pressure control system is formed by the control unit 17, the
fuel pressure sensor 20 and the high pressure regulator 16 at
least.
FIG. 3 shows a diagnosis routine for detecting abnormal conditions
in the fuel system.
At a step S11, the control unit 17 determines whether the pressure
deviation .DELTA.P of the actual fuel pressure FP sensed by the
fuel pressure sensor 20 from the desired fuel pressure tFP is equal
to or greater than a predetermined pressure deviation value
.DELTA.Pa.
When the pressure deviation is equal to or greater than the
predetermined deviation value .DELTA.Pa, then the control unit 17
proceeds from the step S11 to a step S12. At the step S512, the
control unit determined whether this condition in which the
pressure deviation is equal to or greater than the predetermined
deviation value .DELTA.Pa continues for a time duration equal to or
longer than a predetermined time length Tb.
If the duration of this condition of the excessive pressure
deviation is equal to or longer than the predetermined time length
Tb, then the control unit 17 judges that there exists abnormality
in the fuel system, and proceeds from the step S12 to a step
S13.
At the step S13, the control unit 17 commands an engine operation
in a homogeneous stoichiometric combustion mode in which the air
fuel ratio is feedback-controlled to a theoretical air fuel ratio
in accordance with the air fuel ratio sensed by the air fuel ratio
sensor 16. Therefore, the engine 1 is operated in the homogeneous
stoichiometric combustion mode. If the engine operation before the
step S13 is in the stratified combustion mode, for example, the
control unit 17 forcibly changes over the combustion mode, at the
step S13, from the stratified combustion mode to the homogeneous
stoichiometric combustion mode. The control system according to
this embodiment effects the homogeneous stoichiometric combustion
mode in order to locate abnormal conditions as mentioned later, and
further in order to maintain stable driveability. The stratified
charge combustion is readily affected by abnormality in the fuel
system whereas the homogeneous combustion can provide more stable
combustion.
At a step S14, the control unit 17 determines a feedback correction
quantity .alpha. of the feedback air fuel ratio control in the
homogeneous stoichiometric combustion mode. The feedback air fuel
ratio correction quantity .alpha. is determined according to a
predetermined control law (or control action) such as I control law
or PI control law.
At a step S15, the control unit 17 determines whether the feedback
air fuel ratio correction quantity .alpha. is in a condition
sticking to an upper limit value (125%, for example) or a lower
limit value (75%, for example) on either side of a reference value
(100%) corresponding to the theoretical air fuel ratio.
If the feedback correction quantity .alpha. is equal to the upper
or lower limit value, the control unit 17 proceeds to a step S16,
and judges that there is a malfunction in the pressure sensor 20.
When the sensor signal produced by the fuel pressure sensor 20 is
abnormal, the fuel injection quantity calculated from the abnormal
sensor signal is not correct, and the control system is unable to
control the fuel injection quantity properly. Therefore, the
control system increases or decreases the feedback correction
quantity .alpha. in a direction to correct the error. As a result,
the feedback correction quantity .alpha. sticks to, or is held
persistently equal to, the upper or lower limit.
When the feedback correction quantity .alpha. oscillates on both
sides of a middle value without sticking to the upper or lower
limit, the control unit 17 judges that there is no abnormality in
the fuel pressure sensor 20, and that the feedback air fuel control
is normal, and proceeds from the step S15 to a step S17 to judges
that the abnormality is attributable to a malfunction in the high
pressure regulator 16, or bad contact of a connector in wiring
harness or some other causes.
Abnormality in the fuel pressure control system affects control
performance of the air fuel ratio control system. By examining this
relationship, this control system presumes that the fuel pressure
sensor is still functioning properly if the feedback stoichiometric
air fuel ratio control is still in an allowable range.
This engine system can maintain the stability of the combustion by
changing over the combustion mode from the stratified charge
combustion mode, a homogeneous lean combustion mode or some other
lean combustion mode, to the homogeneous stoichiometric combustion
mode when an abnormal condition is detected in the fuel system.
Moreover, the control system can discriminate a malfunction in the
fuel pressure sensor 20 from a malfunction not attributable to the
fuel pressure sensor 20 by monitoring the feedback air fuel ratio
correction quantity in the homogeneous stoichiometric mode.
Therefore, this system can reduce the time required for repair.
The predetermined deviation value .DELTA.Pa used in the step S11 to
determine whether the actual fuel pressure FP is settled down to
the desired fuel pressure tFP may be varied in accordance with the
desired fuel pressure tFP. When the desired fuel pressure is high,
the differential pressure (or pressure deviation) of the actual
fuel pressure from the desired fuel pressure tends to increase.
Therefore, the predetermined deviation value .DELTA.Pa is increased
when the desired fuel pressure is higher, and the predetermined
deviation value .DELTA.Pa is decreased when the desired fuel
pressure is lower. By adjusting the predetermined deviation value
.DELTA.Pa in this way, the control system can accurately detect
settlement or unsettlement of the fuel pressure.
Instead of the diagnostic check in the step S15 shown in FIG. 3, it
is possible to perform a diagnostic operation by checking the
combination of the positive or negative sign of the pressure
deviation .DELTA.P (=tFP-FP), and the positive or negative sign of
a deviation (.alpha.-1) of the feedback correction quantity .alpha.
from a reference value 1. In this case, the control system performs
the feedback fuel pressure control, but the control system does not
perform the correction (or modification) of the basic fuel
injection quantity Tp based on the sensed fuel pressure.
When the fuel pressure sensor 20 is abnormal, and the sensed value
is stuck to an upper or lower limit value, the pressure deviation
.DELTA.P (=tFP-FP) is persistently held negative or positive, and
the feedback fuel pressure control based on this erroneous sensed
fuel pressure causes a decrease or increase of the actual fuel
pressure. In response to the decrease or increase of the actual
fuel pressure, the feedback air fuel correction quantity .alpha. is
increased or decreased to restrain changes in the fuel injection
quantity, and the deviation (.alpha.-1) becomes positive or
negative. Therefore, the control unit 17 judges that there is an
abnormal condition to fix the sensed value of the fuel pressure
sensor 20 to the upper limit value when the pressure deviation
(tFP-FP) is negative and the deviation (.alpha.-1) is positive.
When the deviation (tFP-FP) is positive and the deviation
(.alpha.-1) is negative, the control unit 17 judges that there
arises an abnormal condition fixing the sensed value of the fuel
pressure sensor 20 to the lower limit value.
If, on the other hand, the control duty DUTY for the high pressure
regulator 16 is fixed to the opening valve side, the actual fuel
pressure FP decreases below the desired fuel pressure tFP and the
deviation (tFP-FP) becomes positive. In response to this decrease
in the actual fuel pressure FP, the basic fuel injection quantity
Tp is decreased, the feedback air fuel ratio correction quantity
.alpha. is increased and the deviation (.alpha.-1) becomes
positive.
If the control duty DUTY is fixed to the closing valve side, the
actual fuel pressure FP increases above the desired fuel pressure
tFP and the deviation (tFP-FP) becomes negative. In response to
this increase in the actual fuel pressure FP, the basic fuel
injection quantity Tp is increased, the feedback air fuel ratio
correction quantity .alpha. is decreased and the deviation
(.alpha.-1) becomes negative.
Therefore, the control system judges that there is an abnormal
condition fixing the high pressure regulator 16 to the opening side
when the deviation (tFP-FP) is positive and the deviation
(.alpha.-1) is positive, too. When the deviation (tFP-FP) and the
deviation (.alpha.-1) are both negative, the control system judges
that there is an abnormal condition fixing the high pressure
regulator 16 to the closing side.
The fuel pressure sensor 20 of the illustrated example produce a
voltage signal according to a characteristic shown in FIG. 4. The
high pressure regulator 16 varies the controlled fuel pressure in
accordance with the duty ratio (%) of the solenoid energizing drive
signal as shown in FIG. 5.
FIG. 6 shows, as a more practical example, an engine system which
is almost the same as the system shown in FIG. 1. The engine system
of FIG. 6 comprises a fuel tank (F/TANK), a feed pump (or low
pressure fuel pump) driven by an electric motor, a high pressure
fuel pump driven by a cam shaft of the engine, a high pressure
regulator for controlling the fuel pressure in response to a fuel
pressure control signal sent from a control unit, at least one fuel
injector (F/INJ), and at least one spark plug, as in the engine
system of FIG. 1. A crank angle sensor has a unit for producing a
POS signal to signal each unit crank angle, and a unit for
producing a REF signal for signaling each angular displacement of a
predetermined crank angle. FIG. 6 further shows an injector drive
unit (INJ D/U) for driving the fuel injector, an accelerator pedal
(A/PEDAL) operated by a driver of the vehicle, an accelerator
position sensor for sensing a depression degree of the accelerator
pedal, an electronically controlled throttle valve unit for
controlling the intake air quantity, an air cleaner (A/CLNR), an
air flow meter (AFM), and an O.sub.2 sensor. The control unit
performs the control and diagnostic routines of FIGS. 2 and 3 in
the same manner as the control unit 17 of FIG. 1.
The engine system of FIG. 1 (or FIG. 6) can be regarded as a
control system as shown in FIG. 7.
A section 101 is an input section for measurement of an actual fuel
pressure (FP) supplied to a fuel injector for an engine. The
section 101 corresponds to the step S2. The pressure measuring
section 101 may comprise the fuel pressure sensor 20.
A pressure controlling section 102 produces a feedback fuel
pressure control signal to reduce a pressure deviation of the
sensed (or measured) actual fuel pressure (FP) from a desired fuel
pressure (tFP). The section 102 corresponds to the step S3. The
pressure controlling section 102 may comprises a first subsection
for determining the desired fuel pressure in accordance with one or
more engine operating condition by receiving input information from
engine operating condition sensors, a second subsection for
determining a pressure deviation of the sensed actual fuel pressure
from the desired fuel pressure by receiving the actual fuel
pressure signal from the section 101 and the desired fuel pressure
signal from the first subsection, and a third subsection for
producing the feedback fuel pressure control signal in accordance
with the pressure deviation determined by the second subsection.
The first subsection corresponds to the step S1, and the second and
third subsection correspond to the step S3.
An abnormality detecting section 103 detects abnormality in the
fuel system of the engine by monitoring a settling condition of the
actual fuel pressure toward the desired fuel pressure. The
abnormality detecting section 103 corresponds to the steps S11 and
S12.
A richer combustion mode effecting section 104 functions to cause a
combustion changeover to a richer combustion mode such as the
homogeneous stoichiometric combustion mode if the abnormality is
detected and the engine operation is not in the richer combustion
mode. Preferably, the richer mode effecting section 104 causes a
feedback stoichiometric air fuel ratio control of a homogeneous
stoichiometric charge combustion mode to be performed if the
abnormality is detected. The section 104 corresponds to the step
S13.
A diagnosing section 105 judges whether the abnormality is
attributable to the pressure measuring section 101, by monitoring a
parameter, such as a deviation of the air fuel ratio, indicative of
control behavior of the feedback stoichiometric air fuel control in
the homogeneous stoichiometric combustion mode. The section 105
corresponds to the steps S15.about.S17.
The control system may further comprise one or more of the
following sections, as shown in FIG. 7.
An output section or output device 106 receives the result of the
diagnosis from the section 105. The output section 106 may be in
the form of a warning indicator or warning device for providing
visible or audible warning message about the result of the
diagnosis of the section 105. Alternatively, or in addition to the
warning device, the output section 106 may comprise one or more
components forming a fail-safe system or another engine or vehicle
control system for controlling the engine or vehicle so as to adapt
the engine or vehicle operating conditions to the abnormal
condition determined by the section 105. Moreover, the output
section 106 may comprise a memory device for storing information
about the result of the diagnosis supplied from the section
105.
An actuating section 108 varies or regulates the fuel pressure in
response the fuel pressure control signal delivered from the fuel
pressure controlling section 102. In the example of FIG. 1, the
actuating section 108 comprises at least the high pressure fuel
regulator 16. The actuating section 108 corresponds to the step S4.
For example, the actuating section 108 comprises the high pressure
regulator 16, or only the duty solenoid of the high pressure
regulator 16, or the combination of the high pressure pump and
regulator 14 and 16.
An input section 110 comprises one or more engine operating sensors
and collects input information about one or more engine operating
conditions to determine engine operating parameters indicative of
engine load and engine speed, for example. The input section 110
may comprise one or more of the crank angle sensor, the accelerator
position sensor, and the air flow sensor.
A combustion control section 112 is for controlling the combustion
in the engine in accordance with the input information collected by
the input section 110 and the fuel pressure measuring section 101.
For example, the combustion control section 112 changes over the
engine combustion mode between a first combustion mode and the
homogeneous stoichiometric combustion mode by changing a desired
target fuel/air ratio (or a desired target equivalent ratio) in
accordance with the engine operating parameters. The first
combustion mode may be a stratified charge combustion mode, or a
homogeneous lean combustion mode or some other lean combustion
mode. Specifically, the control section 112 serves as a lambda
controller for feedback-controlling the fuel air ratio of the air
fuel mixture supplied to, or produced in, the engine.
A section 114 comprise one or more actuators for varying the fuel
air ratio, and for achieving a combustion changeover between a
first combustion mode such as the stratified charge combustion mode
and a second combustion mode such as the homogeneous charge
combustion mode by changing the fuel injection quantity, the intake
air quantity and the injection timing, for example.
If the actual fuel pressure is not settled down to the desired fuel
pressure, the control system of FIG. 7 according to the present
invention judges that an abnormal condition has occurred in the
fuel pressure sensor or in the fuel pressure control system, and
changes over the engine combustion mode to the richer combustion
mode, such as the homogeneous stoichiometric charge combustion
mode, in which the feedback air fuel ratio control is performed to
a richer ratio level. By changing over the combustion mode from the
leaner combustion mode such as the stratified charge combustion
mode or the homogeneous lean combustion mode, to the richer
combustion mode such as the homogeneous stoichiometric mode, the
control system can protect stable combustion against
abnormality.
When the deviation of the sensed actual air fuel ratio from the
desired richer ratio such as the stoichiometric ratio during engine
operation in the richer mode such as the homogeneous stoichiometric
mode is large, the control system judges that there is a
malfunction in the fuel pressure sensor. Abnormality in the signal
of the fuel pressure sensor makes the calculation of the fuel
injection quantity inadequate, and hence increases the deviation of
the air fuel ratio. If, on the other hand, the deviation of the air
fuel ratio is small or null, then the control system judges that
there is a malfunction in the fuel pressure control system.
The present invention is advantageous when applied to an
in-cylinder direct injection engine in which higher fuel pressure
is needed for the stratified combustion mode injection on the
compression stroke, and the feedback control of the fuel pressure
is important to adapt the fuel pressure to a desired fuel pressure
varying in dependence on engine operating conditions. However, the
present invention is not limited to the in-cylinder direct
injection engine. The present invention is also applicable to a
lean burn engine, for example.
The present application is based on a Japanese Patent Application
No. 9-232007. The entire contents of Japanese Patent Application
No. 9-232007 with a filing date of Aug. 28, 1997 are hereby
incorporated by reference.
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